PARP1 is a novel genetic interactor of BRCA2

Wednesday, September 24, 2014 — Poster Session IV
10:00 a.m. –12:00 p.m.	FAES Academic Center	NCI	CANCER-9

* FARE Award Winner

Authors

• Xia Ding
• Shyam Sharan

Abstract

Pathogenic mutation of BRCA2 is one of the highest risk factors of developing breast and ovarian cancer. Because BRCA2 loss causes genomic instability, which results in apoptosis or cell cycle arrest in normal cells, mutation in other genetic interactors is required for tumor development. We try to identify novel BRCA2 genetic interactors by using a siRNA library screen in mouse embryonic stem cells (mESC). We utilize mESC genetically engineered to have endogenous Brca2 deleted and carry BAC expressing a hypomorphic mutant BRCA2. These cells are hypersensitive to poly(ADP-ribose) polymerase (PARP) inhibitor (PARPi). After knocking down certain genes, cells gained resistance to PARPi, suggesting these genes may be BRCA2 genetic interactors. PARP1 was one top candidate. Stable knockdown (KD) of PARP1 rescued BRCA2-null mESC lethality. Rescued cells are deficient in homologous recombination (HR) and highly genomic unstable. Rescued cells have increased non-homologous end joining (NHEJ), suggesting increased NHEJ compensates for HR loss. We treated BRCA2-deficient mouse primary breast tumor cells and its wild-type BRCA2 BAC reconstituted counterpart with AZD2281 (PARPi) in combination with DNA-PK inhibitor NU7441. The combination exacerbated killing of only the BRCA2-deficient cells, not its BRCA2 wild-type counterpart. The current study reveals PARP1 as a novel BRCA2 genetic interactor.

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